1. Technical Field of the Invention
This invention relates to a polyethylene composite fiber and a non-woven fabric using the same. More specifically, it relates to the polyethylene composite fiber which can be processed into a non-woven fabric within wider processing temperature range, and of which obtained non-woven fabric has good touch feeling and high strength. Further, it relates to the non-woven using the same and a medical or hygienic material using the non-woven.
2. Description of Related Art
Presently, disposable materials made of non-woven for medical use such as surgical caps, surgical sheets, surgical covering clothes, surgical gowns are spreading rapidly. This is to solve a recent problem of hospital infection such as an infection of MRSA (methicillin-resistant Staphylococcus aureus), hepatitis or HIV (human immunodeficiency virus). Further, using disposable non-woven materials requires no necessity for cleaning, so that nursing work can be simplified without deteriorating nursing quality. Also it can be one of solutions for a labor shortage that has been becoming serious social problem. The non-woven fabric for medical use is required to have bacteria barrier property, anti-permeability, water repellency, lint free property and so on, but also importantly required to have good wear feeling, strong tenacity and cost performance, because the fabric is directly contacted to human body and disposable for only one time use.
As raw materials of fibers for non-woven, polyethylenes, polypropylenes and polyesters are widely used. Concerning to non-woven fabrics for medical use, it is not exceptional to use these resins generally for the raw materials of the non-woven fabrics.
By the way, the non-woven fabrics for medical use are frequently disinfected under radiation, but it is a problem and restricted to use polypropylene resins for usage such as being disinfected under radiation, because the polymer chain is cut resulted from chemical bonds cut on tertiary carbon atoms under radiation, and the non-woven fabric lose their tenacity drastically.
Concerning to polyester resins, radiation dose not weaken their tenacity, but polyester resins cost higher than polyolefin resins. And when polyester non-woven fabric having high basis weight is used to make the fabric tenacious enough to avoid being torn by user""s body action, or to make the fabric being not see-through, the fabric becomes hard and has bad wear feeling, or lacks its light feeling due to the raw material resin""s nature. Because of these problems, polyester non-woven fabrics are not positively used by hospital and inhibitedly do not spread.
Contrary to this, polyethylene resins are suitable for medical use non-woven fabrics, because of some advantage such that soft non-woven fabrics can be produced due to the raw material resin""s nature, and having no tertiary carbon atoms does not weaken the tenacity under radiation.
However, conventional non-woven fabrics composed of single polyethylene component having no composite structure are not suitable for through-air processing method using heated air to obtain non-woven fabrics, the method makes less softness problem of the non-woven fabric.
To solve this problem, for example, Japanese Tokkyo Kouhyou Koho Hei 6-508892 (corresponding to PCT Gazette W093/01334) discloses a polyethylene composite fiber having a high density polyethylene as the first component and a copolymer of ethylene and xc3xa1-olefin (abbreviated as xe2x80x9cL-LDPExe2x80x9d hereinafter) as the second component. But using general L-LDPE as the second component, it is not sufficiently suitable for processing method such as the through-air method, because the melting point difference between both components is still small. Using a L-LDPE having relatively low density, a very low density polyethylene (VLDPE) or an ultra low density polyethylene (ULDPE) as the second component to increase the melting points difference between the first and second components, but with decreasing of the resin density, there has been presently still some problems that the surface of the fibers being stickier, appearance of neps at carding stage, and the tenacity of obtained non-woven fabrics being decreased considerably.
This invention aims to solve the above mentioned problem, and to present a polyethylene composite fiber being usable for thermal-embossing and through-air processing, being possibly used for production of non-woven fabrics having good touch feeling and showing high tenacity, and also to present a non-woven fabric using the same.
The present inventors have diligently made research to solve the above problem of the conventional polyethylene fibers, and have got knowledge that the problem can be solved by a polyethylene composite fiber which comprise a high melting component (B) comprising a polyethylene (b) with specified density, and a low melting component (A) having lower melting point than (B), comprising a polyethylene (a) with specified Q value (number average molecular weight/weigh average molecular weight) polymerized with metalocene catalyst, and have made reduction to practice of this invention.
This invention is characterized that;
1. A polyethylene composite fiber comprising two kinds of polyethylene resin components having different melting points,
wherein the low melting component (A) comprises a polyethylene (a) polymerized with a metallocene catalyst, and having a density of 0.850 to 0.930 g/cm3 and a Q value (number average molecular weight/weigh average molecular weight) of 3.0 or less,
and the high melting component (B) is a polyethylene (b) having a density of 0.940 g/cm3 or more,
2. A polyethylene composite fiber comprising two kinds of polyethylene resin components having different melting points,
wherein the low melting component (A) comprises a polyethylene (a) polymerized with a metallocene catalyst, and having a density of 0.850 to 0.930 g/cm3 and a Q value (number average molecular weight/weigh average molecular weight) of 3.0 or less,
and the high melting component (B) is a polyethylene (b) having a density of 0.940 g/cm3 or more,
and analysis of the fiber using a differential scanning calorimeter (DSC) shows two different endothermic peaks P1 and P2 on the DSC curve from the two components (A) and (B) of the fiber respectively,
and when L1 is defined as the length from the baseline of the DSC curve to the endothermic peak P1, and when W is defined as the length of a linear segment parallel with the baseline, passing the midpoint between the baseline and P1, and crossing the DSC curve,
the relationship of L1 and W is expressed as L1 greater than 3W,
on the proviso that a programming rate is 10xc2x0 C./min., and the DSC chart is so scaled as that the length of 2 W/g scale on the vertical axis (the heat flow scale, unit: W/g) equals to the length of 50xc2x0 C. scale on the horizontal axis (the temperature scale, unit: xc2x0 C.).
3. The polyethylene composite fiber according to the above article 2,
wherein P3 is defined as a point being on the DSC curve between the two endothermic peaks P1 and P2 of the two components and being closest to the baseline, and L2 is defined as the length of a linear segment rectangularly lying from the baseline to the point P3, the relationship of L1, and L2 is expressed as L1 greater than 3L2.
4. The polyethylene composite fiber according to the above article 2,
wherein the polyethylene (b) of the high melting component (B) is a high density polyethylene having a density of 0.945 g/cm3 to 0.965 g/cm3.
5. The polyethylene composite fiber according to the above article 2,
wherein the polyethylene (b) of the high melting component (B) is a polyethylene having a melting point of 125xc2x0 C. to 135xc2x0 C.
6. The polyethylene composite fiber according to the above article 2,
wherein the polyethylene (b) of the high melting component (B) is a polyethylene having a melt flow index of 5 g/10 min. to 45 g/10 min.
7. The polyethylene composite fiber according to the above article 2,
wherein the polyethylene (a) of the low melting component (A) is a polyethylene having a density of 0.850 g/cm3 to 0.930 g/cm3.
8. The polyethylene composite fiber according to the above article 2,
wherein the polyethylene (a) of the low melting component (A) is a polyethylene having a melting point of 70xc2x0 C. to 125xc2x0 C.
9. The polyethylene composite fiber according to the above article 2,
wherein the polyethylene (a) of the high melting component (A) is a polyethylene having a melt flow index of 5 g/10 min. to 45 g/10 min.
10. The polyethylene composite fiber according to the above article 2,
wherein the melting point difference of the two components is 5xc2x0 C. or more.
11. A non-woven fabric using the polyethylene composite fiber according to the above article 1.
12. A non-woven fabric using the polyethylene composite fiber according to the above article 2.
13. The non-woven fabric according to the above article 12, wherein the non-woven fabric is obtainable with spun bonding method.
14. The non-woven fabric according to the above article 12, wherein the non-woven fabric is obtainable with through air processing method that the fiber is thermally melt-bonded one another.
15. The non-woven fabric according to the above article 12, wherein the non-woven fabric is obtainable with point bonding method that the fiber is thermally melt-bonded one another.
16. A medical article using the non-woven fabric according to the above article 12.
17. A sanitary article using the non-woven fabric according to the above article 12.